Intravitreal gene therapy preserves retinal function in a canine model of CLN2 neuronal ceroid lipofuscinosis

CLN2 neuronal ceroid lipofuscinosis is a rare hereditary neurodegenerative disorder characterized by deleterious sequence variants in TPP1 that result in reduced or abolished function of the lysosomal enzyme tripeptidyl peptidase 1 (TPP1). Children with this disorder experience progressive neurological decline and vision loss starting around 2-4 years of age. Ocular disease is characterized by progressive retinal degeneration and impaired retinal function culminating in total loss of vision. Similar retinal pathology occurs in a canine model of CLN2 disease with a null variant in TPP1. A study using the dog model was performed to evaluate the efficacy of ocular gene therapy to provide a continuous, long-term source of human TPP1 (hTPP1) to the retina, inhibit retinal degeneration and preserve retinal function. TPP1^-/- dogs received an intravitreal injection of 1 x 10¹² viral genomes of AAV2.CAG.hTPP1 in one eye and AAV2.CAG.GFP in the contralateral eye at 4 months of age. Ophthalmic exams, in vivo ocular imaging and electroretinography were repeated monthly to assess retinal structure and function. Retinal morphology, hTPP1 and GFP expression in the retina, optic nerve and lateral geniculate nucleus, and hTPP1 concentrations in the vitreous were evaluated after the dogs were euthanized at end stage neurological disease at approximately 10 months of age. Intravitreal administration of AAV2.CAG.hTPP1 resulted in stable, widespread expression of hTPP1 throughout the inner retina, prevented disease-related declines in retinal function and inhibited disease-related cell loss and storage body accumulation in the retina for at least 6 months. Uveitis occurred in eyes treated with the hTPP1 vector, but this did not prevent therapeutic efficacy. The severity of the uveitis was ameliorated with anti-inflammatory treatments. These results indicate that a single intravitreal injection of AAV2.CAG.hTPP1 is an effective treatment to inhibit ocular disease progression in canine CLN2 disease.